P2 Locomotive Company and related matters

I thought there were problems on 2002 with smoke not clearing, attributed to the softer exhaust of the Walschaerts gear. They tried to solve the problem with additional smoke deflectors which looked hideous. The improved Lentz gear seems the best bet to me.

Dave

 

The repeat of the 2001 smoke box and deflecting front end design did not prove satisfactory when applied to 2002. The softer exhaust experienced on this second machine proved troublesome and so supplementary deflector plates were tried but the ultimate solution was the A4 Bugatti form which is now so familiar.

The sharp exhaust experienced on 2001 was a significant factor in the fuel consumption levels experienced with this engine. The decision to base 2007 on the class prototype is at one level understandable, such a distinctive machine. Attending to the modifications to be made to improve the chassis of the design will not be particularly onerous - some of what was required was identified 70 and more years ago. Maintaining the tractive effort figure while endeavouring to offer improved route availability, again no great issue.

Introducing a design of poppet valve gear that does not display the weaknesses of the original is another matter. Lentz suffers from excessive wear, B.C. and the inside cylinder hits another hurdle. So Franklin patents are being looked at. If a mechanism can be introduced that does not exhibit the weakness of a very small contact area on the rotating cam mechanism all well and good. If it can be fitted within the limitations of the design even better. How much trailing on preserved lines the locomotive will have to undertake before anyone might consider it fit for the mainline, if fitted with something unique in the valve gear field, is another potential obstacle.

 

That's an interesting point about 2007 having to prove its fitness for main line operation.

However, my understanding is that Franklin developed the Lentz gear into a reliable system. After a quick google I can't remember where I read this though.

So if it was used on the original (albeit with mixed results), as well as successfully on the D49s and in the states, can it really be said to be unique?

Dave

 

Drifting smoke? Nothing that a good thumbprint behind the chimney won't cure............

Cheers,

Alan

 

Yes but much of the smoke deflection issue was potentially with the softer exhaust of the walschaerts in combination with the double chimney setup. This could in theory have been solved with a Lempor exhaust instead. That then raises the question of how far do you go away from the original design, etc...

It's an interesting debate to be had that's for sure.

 

double vs Lempor??? Please explain!
Kind regards
Jos Koopmans

 

But was that not down to having stepped rather than continuous scroll cams? Often if one setting was insufficient then the next step up was too much and tore the fire apart. What fuel consumption figures has 71000 achieved with its continuous scroll cams?

 

As I understand it, using a Lempor exhaust combined with the Walschaerts valve gear might give a combination whereby the exhaust is not as soft as the Kylchap, thus contributing to smoke deflection. That essentially is the problem with the double chimney and in particular the Kylchap the LNER employed on their Pacifics. The A4s of course had the wedge shaped front end which is the best for smoke deflection but on all other engines deflectors were required.

 

Not forgetting the Thumbprint, of course...............

Cheers,

Alan

 

A Lempor is an incremental improvement over a Kylchap, and it is also low-backpressure device so I wouldn't expect it to 'throw' the exhaust any higher than a Kylchap, and a double Kylchap ought to outperform a single Lempor in terms of efficiency.

 

My comment would be almost identical, a more efficient exhaust system leads to lower chimney exit velocities and, as a consequence, to more trouble breaking through the low pressure areas around a non-streamlined locomotive smokebox.
What I do not understand that, given the succesful NACA cowling around radial engines, the flow arrangement remained so poorly for locomotives, it is the same problem isn't it?
Kind regards
Jos Koopmans

 

Fair enough Sheff, my apologies.

 

And going back to 1930's applications of 'exhaust systems' regardless of type single or double we're a little haphazard. A perfectly sized single exhaust will give better results than a single/double/ triple kylchap/kylpor/Lemaitre/ lempor/ lemprex / geisl etc that is the incorrect size.

 

Hmmm, I am inclined to challenge that statement.Mainly because they did not know what the perfect single dimensions were and secondly because an incorrect sized multiple is more forgiving as it is already an improvement.
Kind regards,
Jos Koopmans

 

2001 when in original condition suffered from high fuel consumption because of the nature of the exhaust discharge. When considering modern piston valve designs due consideration has to be given to the nature of the exhaust release, some favour a clean, rapid release though the impact of this is not viewed by all as being the best for overall efficiency because of the impact that it has on the fire and on the condition known as carryover and so a more controlled release is also argued for. One aspect of 2001 that was highly thought of was a feature of the valve gear; when in mid gear the inlet valves remained closed and the exhaust valves open - the machine drifted very freely. Clearance volumes were never satisfactory, 2002 was a vastly superior machine in this regard, the original infinite variations were lost when stepped cams had to be introduced. High temperatures were found in the cambox and these did nothing to help with the high wear that forced the change from the original arrangement. An oil cooling system was tried for a period.

The high exhaust peaks could be dealt with by means of attention to a new exhaust system design but the effect of this would be to place 2007 in the state that 2002 was found to be in when first built. The Trust wants the distinctive appearance of 2001 as it originally designed. Achieving this could prove interesting to say the least.

The B.C. gear is very different to the Lentz and the LNE got the Caprotti gear working rather well before WW2.

 

You'll have to explain that I think. My very inexpert understanding of the challenges of radial cowling design is that one wishes to combine low drag with a generous supply of cooling air to the cylinders within the cowling, all operating in a flow of highly disturbed air at considerable speed, being in the wake of the airscrew. Its not obvious, to me at least, how this relates to smoke clearance on a locomotive smokebox.

 

Yes Jos, but sometimes by luck if nothing else good proportions we're found and ill proportioned 'improvements' were of no benefit. The Schools Class being the example I had in mind....

 

One should see the similarity between a radial engine and a smokebox front: both are blunt objects in a flow. When the flow is pushed around the edges large vortices/eddies are created with pockets of lower pressure that can suck smoke gases in the case of the locomotive.
The radial engine is remedied with the NACA cowling that guides the air flow to cool the cylinderheads. The locomotive gets smoke deflectors that guide and straiten the flow at the boiler side and push excess air upwards. However at the smokebox top the problem is still there and a chimney which is too close to the smokebox (MN, BB/WC) or has a low exit velocity still faces problems.
Kind regards
Jos Koopmans

 

Sure ive touched on this before on this thread. The sugar scoop idea employed by Bulleid on the P2 and initially on the Merchant Navies didn't work well as a 'Smoke deflector'; Rather it creates a partial vacuum down the sides of the boiler which draws the smoke and steam back down the sides. The anticipated entrainment or blasting clear as the design intends might start to occur higher running speeds... who can say
Creating a ' Gill-slit' should help with this without much alteration to the appearance. Perhaps Mr Elliott has already got some of his aerospace buddies to check the arrangement out ?

 

If the exhaust valves stay open as the pistons move to and fro (and presuming that the blower is on to keep some draught on the fire) how do you prevent smoke and small particles of coal getting drawn into the cylinders?